ROME — Having floated for at least two days in the choppy Mediterranean Sea to reach Europe, a rickety trawler overstuffed with African migrants fleeing war and poverty was nearing a Sicilian island, not even a quarter-mile away. But it was still dark and no one had yet spotted them. So to signal their position, someone set a match to a blanket.

But rather than sending a signal, the fire brought tragedy when flames from the burning blanket ignited gasoline. Nearly 500 people are estimated to have been on board — including children — and the blaze created a panic that capsized the boat. So close to reaching land, the migrants were now tossed into the sea. Many could not swim.

The accident, which occurred before dawn on Thursday within easy eyesight of the island of Lampedusa, is one of the worst in recent memory in the Mediterranean: at least 111 people were reported dead, with up to 250 still missing. At least 150 others survived, and Italy’s Coast Guard was continuing to search for more survivors.

The grisly deaths again underscored the dangerous, desperate efforts by many migrants from Africa and the Middle East to reach Europe by sea, while also renewing criticism of European immigration policy. Immigration is a politically volatile issue in Europe, so much so that Greece recently completed a nearly eight-mile fence blocking its border with Turkey, an attempt to shut down a major land migration route.

But some experts say that making it harder to slip into Europe by land has only pushed many migrants to try the more perilous route by sea. With conflicts raging in the Middle East and Africa, the number of asylum seekers and migrants arriving by boat in Spain and Italy has spiked this year. According to statistics released by Save the Children, 21,780 migrants reached Italy during the first nine months of this year, including 4,000 children.

Lampedusa, an Italian island barely 70 miles from northern Africa, has become a gateway to Europe for migrants. In some seasons, boats filled with migrants and asylum seekers arrive almost daily.

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About 500 people were said to be on a boat bound for Italy.Credit
The New York Times

Pope Francis, who visited the island in July to draw attention to the plight of migrants, expressed sadness and outrage over Thursday’s fatal accident.

“The word disgrace comes to me,” the pope said during an audience, calling for prayers on behalf of the dead and their families. “Let us unite our efforts so that similar tragedies do not happen again. Only a decided collaboration among all can help to stop them.”

For Italy, the flow of migrants across the Mediterranean has become an enormous operational and humanitarian challenge. Italian Coast Guard boats are sent almost daily on dangerous rescue missions. Migrants assume huge risks to reach Europe and pay thousands of dollars to smugglers and middlemen, often in Turkey, Egypt and Libya. The smugglers load people onto a large boat for a trip into Italian waters. There, the migrants are usually transferred to smaller boats, some barely seaworthy, and left to float in the current. Then the smugglers flee back to Africa.

It was unclear if the migrants in Thursday’s accident were delivered by smugglers and then transferred to a smaller boat, or if they made the entire journey from Libya in the same trawler. It did seem clear, though, that they were completely unprepared.

“Normally, these boats have a satellite phone, or someone on board will call a relative in Italy who alerts the authorities,” said Veronica Lentini, who works with the International Organization for Migration in Lampedusa, and spoke with several survivors. “But in this case, no one advised anyone.”

Survivors told Ms. Lentini that their ship had traveled from Libya and was a short distance from a tiny sister island of Lampedusa when the engine broke down. Soon, the ship began to take on water, and the fire was started to attract attention. But gas from the broken engine was ignited by the flames, and terrified passengers raced away from the explosion, to one side of the vessel, causing it to capsize.

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The bodies of those killed when a boat packed with migrants caught fire then capsized as it approached Italy’s Lampedusa Island.Credit
Antonio Parrinello/Reuters

Lillian Pizzi, a psychologist working with migrant families on Lampedusa, said the survivors were in a state of shock.

“They’re exhausted and they’re finding it difficult to explain exactly what happened,” said Ms. Pizzi, who works for Terre des Hommes, a nonprofit group. She added: “It is something that happens all too often. It has to be read politically. This is not an accident at sea. It is something else.”

In Rome, Interior Minister Angelino Alfano said that the vessel had departed from Misurata in Libya, and that most of the passengers were from Eritrea and Somalia. No one onboard had a mobile phone, and he confirmed that gasoline was to blame for the rapid spread of the fire.

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“It happened close to shore,” Mr. Alfano said. “Had they been able to swim, they would have been safe.”

Mr. Alfano said Italian rescue boats had been sent as soon as the fire was spotted, and he called on European officials to find solutions to prevent such disasters. “Europe must realize it is not an Italian drama but a European one,” he said during a news conference. “Lampedusa must become the border of Europe, not Italy.”

The death toll was high on Thursday, and could potentially go much higher, but such fatal accidents are hardly rare in the Mediterranean. According to the International Organization for Migration, roughly 25,000 people have died in the Mediterranean in the last 20 years, including 1,700 last year. This week, 13 men drowned near the shore of southern Sicily.

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First responders brought the bodies of drowned migrants to shore from a Coast Guard boat on Thursday in Lampedusa, Italy.Credit
Italian Army, via European Pressphoto Agency

Bruce Leimsidor, an expert in European asylum law, said that many complex factors contributed to such deaths, and that the new wall in Greece was probably contributing to the increased activity on the Mediterranean.

“It’s like trying to hold a balloon under water,” said Professor Leimsidor, who teaches at Ca’ Foscari University in Venice. “The only thing Europe can do is basically take people and give them decent asylum procedures.”

On Thursday, European Commission officials expressed sadness about the accident and blamed criminal syndicates and human smugglers for exploiting desperate people. They called for a crackdown on the smugglers while saying that Europe also needs to step up dialogue with the countries from which migrants originate.

“No country can solve migratory flows by itself,” said Michele Cercone, a spokesman for Europe’s home affairs commissioner. “This won’t end overnight. We have to put in place new tools, new policies to manage better, and we have to do it at a European level.”

But finding a unified immigration policy is difficult, given that member states have different attitudes and policies toward immigrants. And many advocates for migrants said the European Union had done too little to open legal channels for people to migrate, especially those who are not wealthy or educated, and also needed to improve resettlement programs for refugees and asylum seekers.

“Even people who aren’t engineers have reasons to want to have a good life, and come to Europe, a place of safety and opportunity,” said Philip Amaral, advocacy and communications coordinator for the Brussels-based Jesuit Refugee Service Europe. For many, he said, “the only option is to take a risky trip.”

Correction: October 3, 2013

A picture with an earlier version of this article was published in error. It showed a boat that ran aground off the coast of Italy on Monday.

Gaia Pianigiani contributed reporting from Siracusa, Sicily.

A version of this article appears in print on October 4, 2013, on Page A1 of the New York edition with the headline: Migrants Die as Burning Boat Capsizes Off Italy. Order Reprints|Today's Paper|Subscribe